Dissertation Defence: Blood rheology on blood flow during plasmaspheres, plasma contraction, exercise, and chronic hypoxia

Andrew Steele, supervised by Dr. Philip Ainslie, will defend their dissertation titled “Blood rheology on blood flow during plasmaspheres, plasma contraction, exercise, and chronic hypoxia” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Kinesiology.

An abstract for Andrew Steele’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.

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Abstract

Blood rheology properties—including whole blood viscosity, plasma viscosity, and red blood cell (RBC) deformability and aggregation—are key regulators of blood flow and vascular function. Blood viscosity increases blood flow resistance but also contributes to shear stress, a key determinant of vascular resistance and diameter. RBC deformability and aggregation underlie the shear-thinning behaviour of blood, allowing blood viscosity to adjust with changing shear rates. However, the extent to which blood rheology regulates blood flow in humans remains poorly understood. This dissertation aimed to examine how acute elevations in blood viscosity (Study 1) and RBC deformability (Studies 2 and 3) influence vascular perfusion and reactivity under distinct physiological and environmental conditions, including plasmapheresis, plasma contraction, exercise, and chronic hypoxia. Study 1 induced hemoconcentration through plasma donation and diuresis to assess its effects on brachial artery blood flow and reactive hyperemia flow-mediated dilation (RH-FMD). While increased blood viscosity did not alter brachial artery blood flow or RH-FMD, plasma donation and not diuresis enhanced microvascular function, as assessed by reactive hyperemia. Study 2 examined the impact of handgrip exercise and phosphodiesterase-5 (PDE-5) inhibition with sildenafil citrate on RBC deformability, brachial artery blood flow, and cerebral blood flow (CBF). Exercise increased RBC deformability, and sildenafil citrate prolonged this elevated deformation; however, these changes did not affect basal CBF, brachial artery blood flow, or exercise hyperemia. Study 3 evaluated the effects of pentoxifylline, a non-specific PDE inhibitor, on blood rheology, cardiac output, and CBF at high altitude. Chronic hypoxia increased blood viscosity and reduced RBC deformability, but pentoxifylline had no significant effect on blood rheology, CBF or cardiac output. In summary, while physiological and environmental stressors altered blood rheology, these changes did not significantly influence blood flow or vascular reactivity in healthy individuals.